# All Questions

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### Interpretation of Bi-207 decay spectrum

I measured the decay spectrum of Bi-207 as a beta source with scintillation detector and now I am trying to interpret the information given by the spectrum. As far as I know, the Bi-207 nuclei decay ...
2answers
86 views

### Preparing For Jackson Electrodynamics [duplicate]

Hypothetical Scenario: You are an undergraduate physics student who has never taken a course on E&M and you are enrolled in a graduate Jackson electrodynamics course. In general you are good at ...
1answer
73 views

### Do pure states actually exist?

Is it possible to ever actually measure something so precisely that it actually collapses to a pure state, or do we really just get arbitrarily close? If a wavefunction never actually collapses to a ...
0answers
25 views

### Could time also be accelerating similar to the Universe's expansion in 3-D? [on hold]

Since the Universe is made up of 3-D space, it's easy for me to visualize that time is just a 4th dimension. It makes sense to think that since the 3 dimensions we can see are accelerating in their ...
3answers
53 views

### Difference between eigenstate and basis vector?

My understanding is that any wavefunction can be decomposed into a linear sum of basis vectors, which for momentum are something like sine waves and for position are delta functions. And then ...
2answers
59 views

### How can this represent the wave function?

How can $\psi=Ae^{i(kx-\omega t +\phi)}$ represent a plane wave travelling in $+x$ direction? I knew the equation $\psi = A\cos(kx - \omega t + \phi)$. I also know Euler's identity and that the ...
0answers
21 views

### Restriction on the value of adiabatic exponent

My instructor stated in his lecture that the maximum value of the adiabatic exponent, $\gamma$, can be 5/3 which is that of a monoatomic gas, but why is this so? He also stated that this can be found ...
1answer
30 views

### How do molecules gain kinetic energy from light?

I know that molecules can absorb light through electronic and vibrational excitations, which certainly increase the internal energy of a molecule. This idea is always connected to the quantum theory ...
0answers
14 views

### Planck length and photon [duplicate]

With what probability, i.e. a real number in [0,1],a photon occupies a space of the size of Planck length?
0answers
22 views

### Tension due to unequal forces on a massless spring [duplicate]

When a massless spring is pulled by 5N on both sides the tension in the spring is 5N (proved by considering COM at rest and breaking the spring into two springs of 2k each)...what if the forces ...
0answers
33 views

### Photon size vs. Planck length [duplicate]

Another attempt to pose a correct question: with what probability, i.e. a real number in $[0,1]$ photon hits a sphere with diameter the size of Planck length?
1answer
30 views

### Some confusion in Drude theory of metals

Discussion on the drude theory of metal usually begin with the case of zero magnetic field so that the force acting on the electrons is just the one from the electric field. But then, this electric ...
0answers
17 views

### The thickness of the hot air layer above a hot metal

I need a simple way to estimate the thickness of the hot air layer above a metal heated up by about 100K above the room temperature. I'm not sure how to go about estimating this. What happens there, ...
0answers
22 views

### Magnet oscillation with coils

I am trying to conduct an experiment in which I will try to find the natural frequency of a cantilever. To oscillate the cantilever, I thought I could use a magnet and a current-carrying coil wire ...
1answer
37 views

### Why does a water jet bend in a static electric field? [duplicate]

The phenomenon is shown for example in this video where a thin water jet is formed by letting water fall from a small hole punched under a plastic cup, and the jet is bent when a charged rod is moved ...
0answers
10 views

### What is the physical meaning of a molecular fragment having two appearance energies?

Appearance energies are particularly import when it comes down to mass spectrometers that use electron impact bombardment. They typically denote the quantum energy value for fragmenting the molecule ...
0answers
30 views

### How do materials absorb light

I'm curious how light is absorbed in materials. From what I understand, when an electron absorbs a photon, it gets excited to an energy level that is higher than the level it's in and the energy ...
2answers
77 views

0answers
16 views

### Primordial dark matter synthesis

In standard cosmology, there is a general picture of: Primordial nucleosynthesis, i.e., when and how, nuclei or elements were formed. It is not quite tested, but it is more or less known where it ...
1answer
24 views

### Is their a theoretical minimal amout of energy to keep some information?

The goal here is to keep a bit of information $b$ at the temperature $T$ during a time $\delta t$. I don't know if this question makes a lot of sense, considering the diversity of ways to encode ...
3answers
92 views

### Schwarzschild Radius of a Galaxy

If an ultra compact/dense Galaxy has a Schwarzschild radius same as it is own radius, how can it be observed from the outside of the Galaxy?
0answers
19 views

### Does diffusion of matter (Fick s law) happens at null temperature?

If yes : is diffusion of matter due due temperature ? Why the formula does not include temperature ? Thank you
1answer
45 views

### Where does the concept enthalpy come from and what does it mean?

I am reading many online references, but I cannot understand where the concept enthalpy comes from and what it represents. The Spanish Wikipedia article states it is the Legendre transformation of ...
2answers
36 views

### Beam momentum positive/negative sign

Could anyone explain to me why the momentum of this isostatic beam in $A$ is negative instead of positive? Why isn't it as simple as $+FL-FL/2 = +FL/2$?
0answers
31 views

### How much electrical energy can i recover from a heat source at 65 deg Celsius

I am new to the forum and I have been looking around to get a sense of the total waste enegery recoverable from solar cells. We have a pretty sunny climate and the solar cells which covers 600 m$^2$ ...

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